1. Field of the Invention
The present invention relates to a method for analyzing a metal element on a surface of a wafer.
2. Related Art
In recent years, while needs for achieving the increased integration of the semiconductor devices are growing, miniaturization of devices is increasing. On the other hand, required level for the cleanliness in semiconductor manufacturing process tends to become severer and severer. Control of the cleanliness on the surface of semiconductor substrate is a critical issue that influences a production yield of the products. In particular, since a metal impurity remaining thereon may possibly deteriorates electric characteristics of the devices, extremely high cleanliness is required. Analysis technique for precisely detecting and quantifying an impurity on a wafer surface is first required in order to reduce the amount of the impurity. In addition, a process for employing a high-k material for a gate insulating film or a capacitance film of a capacitor recently becomes to be adopted. In addition, metal elements such as ruthenium (Ru) and the like become to be employed as an electrode material. The utilization of new materials provides diversification of metal elements as the evaluation targets. Thus, methods for detecting the various metal elements with higher sensitivity are demanded.
The method for analyzing metal element on wafer surface generally includes a method for chemically analyzing thereof by dissolving a native oxide film generated on the surface with hydrofluoric acid vapor or the like to recover the existing contamination metal included on the surface or in the interior of the native oxide film and analyzing the metal including the recovered solution by atomic absorption spectrometry (AAS), inductively coupled plasma quadrupole mass spectrometry (ICPQMS) or the like. Japanese Patent Laid-Open No. 1990-28,533 discloses a technique, in which metal elements on the wafer surface are dissolved into a solution containing about 0.5 to 2 wt % of HF and the dissolved elements are recovered, and the recovered elements are analyzed by a chemically analyzing method.
The methods for analyzing the local contamination on the surface of the device includes a physically analyzing method for analyzing thereof by total reflection X-ray fluorescence spectrometry (TXRF), secondary ion mass spectrometry (SIMS) or the like. Japanese Patent Laid-Open No. 2004-28,787 discloses a technique for analyzing a metal element on a surface of a wafer by TXRF. According to Japanese Patent Laid-Open No. 2004-28,787, TXRF is a method for detecting fluorescent X-ray emitted from a measurement surface of an object when excited X-ray having better natural collimation is incident upon the measurement surface of the object at a lower incident angle equal to or less than a critical angle that is determined by a wave length thereof and kind of element. In Japanese Patent Laid-Open No. 2004-28,787, an etching vapor, which is generated by heating an etching solution, is in contact with a surface of a silicon wafer to form liquid droplets of the etchant solution containing the metal contaminants. Then, the liquid droplets are dried at their original positions to form residues having fine particle shapes. Then, X-ray is irradiated upon the silicon wafer, and fluorescent X-ray from the residues can be analyzed with information of their position by the total reflection X-ray fluorescence spectrometry.